Preparation Of Modified Porous Carbon Materials And Their Properties In Li-Ion Capacitors

Lithium-ion capacitors（LICs）are considered one of the most promising high-performance energy storage devices.However,achieving high energy density at high power density remains a challenge for current LICs,due to the mismatch of electrode kinetics and capacity between anode and cathode.The development of advanced electrode materials is one of the effective ways to solve the above problems.In recent years,porous carbon materials have attracted extensive attention for LICs,thanks to their high specific surface area,good physical/chemical stability,adjustable internal structure and chemical compositions,and a wide range of source characteristics.In order to meet the different requirements of the cathode/anode of LICs for porous carbon materials,it is necessary to prepare porous carbon materials with suitable porous structure,good electrical conductivity,and heteroatomic doping.Therefore,this paper optimizes the electrochemical properties of porous carbon materials from the perspective of porous structure,heteroatomic doping,and electronic conductivity,so as to build high-performance LICs.The main research contents are described as follows:（1）Chitosan was used as a carbon source and self-doped nitrogen source.The graphene-like nitrogen-doped porous carbon nanosheets（PCNS）were prepared using a simple one-step carbonization method.Abundant mesoporous were introduced into the materials by the Zn O nano-particles that in-situ generated during the carbonization process,and the specific surface area of the materials was effectively improved(PCNS-6,1321.3 m² g^-1).The large specific surface area and well-developed mesoporous provide sufficient adsorption sites and convenient channels for the ions during the electrode process.In the electrochemical test of half-cells,the PCNS-6 shows excellent specific capacity and rate performance when used as the cathode and anode of LICs,and the average specific discharge capacity is 50.0 m Ah g^-1 and 285.1 m Ah g^-1 at 20 A g^-1,respectively.The assembled double-carbon-based LIC that uses the PCNS-6 material as both cathode and anode achieve a high energy density of216 Wh kg^-1 with a high power density of 225 W kg^-1.（2）The cathodes of LICs have much lower specific capacity than the anode,and the energy density of present LICs is severely limited by the carbon-based cathode.In order to design the cathode with high specific capacity,porous carbon material with abundant structural defects and high-level of pyrrolic-N doping was prepared,using polypyrrole as a carbon source and self-doped nitrogen source,by low-temperature activation strategy.It was then self-assembled with two-dimensional reduced graphene oxide（r GO）by a simple one-step hydrothermal method.And the composite with three-dimensional hierarchical porous structure and conjugate conductive network was formed.The highly defective structure provides abundant electrochemical active sites for the electrode process,which enhances the ion adsorption performance.In addition,the three-dimensional hierarchical porous structure and conjugate conductive network structure provide fast ion/electron double transport channels for the electrode process,which synergistic effect promotes rapid ion storage/release,thus greatly improving the rate performance of the cathode.The N-TPC-6/r GO-1.5 cathode has a high specific capacitance of 160.6 F g^-1 at 0.3 A g^-1,and the capacitance retention is as high as 56.6%even at 60 A g^-1.（3）Based on the advantage of high pyrrolic-N content,the polypyrrole polymer is still used as a carbon source and self-doped nitrogen source,and ammonium polyphosphate is introduced as a phosphorus source and additional nitrogen source to prepare the nitrogen and phosphorus co-doped porous carbon nanoparticle.The carbon material with high content of pyrrolic-N doping and the carbon material with high content of phosphorus and pyridinic-N doping were successfully prepared respectively by simple adjustment of carbonization temperature.By introducing abundant electrochemical active sites and increasing the diffusion rate of Li⁺,P-doping not only enhances the storage of Li⁺in the anode material but also improves the kinetic rate of the anode.The 8-PNC anode with the highest content of P-doping has the highest discharge specific capacity of 1130 m Ah g^-1 at0.1 A g^-1.The high content of pyrrolic-N doping is more conducive to enhancing the adsorption of PF₆^-anion on the surface of the cathode,and then improving the specific capacity of the cathode.The 4-PNC cathode with the highest content of pyrrolic-N doping has the highest discharge specific capacity of 111.1 mAhg^-1 at 0.1 Ag^-1.